The role of digitalis drugs in controlling ventricular ectopic activity (VEA) will be studied. Acetyl strophanthidin titration will be employed to screen responders from non-responders. The clinical factors associated with VEA suppression will be sought. Studies will be conducted to determine whether the antiarrhythmic effect of acetyl strophanthidin can be replicated by digitalization with digoxin. It is hypothesized that the action of digitalis drugs in diminishing or eliminating VEA relates to glycoside induced enhancement of vagal action and thereby reducing sympathetic tone. This hypothesis will be tested in two ways: 1) by correlating the digitalis-induced effects on VEA to antiarrhythmic action resulting from the use of vagotonic agents such as phenylephrine and edrophonium; and 2) by determining, through vagal maneuvers whether patients with vagotonia are more susceptible to digitalis drug-induced reduction of VEA. Drug-drug interaction between digoxin and conventional antiarrhythmic agents will be defined utilizing acute drug testing and maintenance therapy with these agents.